# All Questions

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331 views

### Desktop software with HPC resources for back end number crunching

Our workgroup produces a desktop application that simulates building energy performance. It is a .NET application and when the user is running a lot of simulations, they can be quite time consuming. ...
1k views

### Can gsl be compiled with the intel C compiler?

The library itself compiles just fine with icc, but when I try to link to it (using icc for both the driver code and the linker), I get the same error that this question on stackoverflow is asking ...
528 views

### PETSc's makefile system can't find MKL

I'm learning PETSc and trying to make the examples written in C. However, when I use the provided makefile, I get the following error: ...
152 views

### Introduction for (numerical) linear algebra of random variables

I am in search of an introduction into numerical linear algebra - or, at least, pure linear algebra - that treats the case when the input data are random variables. A typical application would be to ...
5k views

### cholesky factorization of block matrices

I have a block matrix (either 2x2 blocks or 3x3 blocks) which is the covariance matrix for a joint space of two or three multivariate normal variables. ie ...
162 views

### nuclear reaction fluid modelling

I'm pretty ignorant regarding the dark arts of numerical codes and modelling, but i'm interested in trying to pursue it for a particular pet project. It regards modelling of nuclear reactions like ...
542 views

### Stability of forward euler method

I am trying to understand the stability of the forward Euler method. I read there's a model problem to see the stability. $$y'(t) = \lambda y(t) \qquad t \in (0, \infty)$$ $$y(0) = 1$$ then the book ...
55 views

869 views

### Where can I find Ansys Fluent for ubuntu?

I am new to Ansys Fluent (the Ansys CFD product). Is it a windows-only software? My institute owns copies that work on windows only. Online tutorials on how to install Fluent on ubuntu aren't clear.
335 views

### Solving PDE or eigenvalue problems without FEM

Do you know any methods/solvers for PDE or eigenvalue problems like $\begin{cases} \Delta u= 0\ (\text{ or }\lambda u) & \text{ in }\Omega \\ u =0 & \text{ on }\partial \Omega \end{cases}$ (...
536 views

### ENO/WENO vs monotone Hermite interpolation

I have see the method PCHIP in matlab that implements the monotone Hermite interpolation method which was originally proposed by Carlson in 1980s. It seem to accomplish the goal of preventing the ...
853 views

### Full Multigrid convergence is too slow. What could possibly be causing it?

I've coded full multigrid in Matlab and it doesn't seem to be converging fast enough. When I increase the number of grids or the number of iterations, it converges to the analytical solution. But FMG ...
110 views

### exact area resampling [closed]

I do image processing, and right now I need to resample some images taken from slightly different perspectives so I can match up features. The pixel intensities have scientific significance, so I want ...
93 views

### System of non-linear ODEs and estimating unspecified initial conditions on Maple 12

I have the following 1st order equations and need to solve them using Maple 12. There are unspecified initial conditions and can only be estimated through the Newton raphson method. My problem is how ...
101 views

### classification machinery needed

Consider a set of 7D vectors. Each vector belongs to one of four classes. After mapping to 3D with PCA and coloring each point according its class the dataset looks like as shown below: For the ...
2k views

### How to determine if a numerical solution to a PDE is converging to a continuum solution?

The Lax equivalence theorem states that consistency and stability of a numerical scheme for a linear initial value problem is a necessary and sufficient condition for convergence. But for nonlinear ...
5k views

### uniform vs. non-uniform grid

It is probably a student level question but I can't exactly make it cleat to myself. Why is it more accurate to use non-uniform grids in the numerical methods? I am thinking in the context of some ...
725 views

### how to visualize lattice with periodic, helical, etc. boundary conditions?

I am trying to write a special hexagonal lattice generator, with several kinds of boundary conditions, such as helical BC, periodic BC, and I find it hard to verify whether it works correctly. I tried ...
3k views

### What algorithm to use for parallel dense matrix inversion on at most 8 cores?

I need to implement parallel dense matrix inversion for a language I am using that appears to not have an existing library for this (specifically IDL using IDL Bridge for message passing). I am ...
191 views

### intuition behind the different discrete norms for Crank Nicolson

I am solving a heat equation $u_t=Au$ with Crank-Nicolson finite-difference method and $A$ is a usual discretization matrix for $u_{xx}$ term. I want to tell something about the whole error vector ...
146 views

### Testing and visualizing large index arrays

I will be implementing nodal discontinuous Galerkin method soon, and having done this before I know the basic indexing arrays I will need to compute, given a mesh and polynomial data. The problem I ...
171 views

### Numeric solution of simple but possibly singular linear system

I have a simple (and small) linear homogeneous system $Ax=0$, where the entries of the $N\times M$ matrix $A$ are small integers. I do not need fancy methods which efficiently solve almost singular ...
131 views

### Extreme points from constraint expression of convex space

I'm looking for the extreme points of the convex set $S\subset [-1,1]^{n\times 3}$ with $r\in S$ such that $$r_{i} \ge r_{k} \iff i\ge k,$$ where the first inequality ...
217 views

### computation complexity of OLS in estimating a VAR model

Could someone tell me the computation cost of using Ordinary least squares in estimating a Vector autoregression model? I am thinking the cost is O(n) where n is the number of the training instance. ...
749 views

### Hamiltonian Matrix Size in Schrodinger Equation

I'm attempting to solve the particle-in-a-box problem using Scipy (with the help of http://www.physics.buffalo.edu/phy410-505/2011/topic4/app2/index.html). At first, I used a 16x16 matrix to model the ...
1k views

### How exactly does the *full* multigrid algorithm run?

So I understand (or at least I believe I do) how a V-cycle runs. I've written in Matlab the 1-D, recursive version of a V-cycle. However, when I ran my code for FMG, my solution wasn't converging. I ...
2k views

### Shape regularity in higher dimensions

In Finite Element theory, and other methods in scientific computing for PDEs, one uses meshes which fulfill several regularity criteria, many of them being equivalent. It is of interest to have ...
354 views

### Limitations of Domain Decomposition Method (DDM) in Finite Element Analysis (FEA)?

The use of DDM in FEA makes parallel solution of the whole analysis e.g. assembly, solver etc possible. DDM splits the model in domains and runs them in parallel. Since there are interconnected nodes ...
232 views

814 views

### What is the best way to get erfi with scipy?

I want this: http://mathworld.wolfram.com/Erfi.html But apparently scipy does not have this in its extensive special functions library. http://docs.scipy.org/doc/scipy/reference/special.html It is ...
154 views

### Approximation of a linear function with polynomials of degree 1

If I have the following problem $$-\mu u'' + u' = 1$$ with boundary conditions $u(0) = u'(1) = 1$ in the interval $\Omega = (0,1)$. The exact solution is $$u(x) = x + 1$$ Will the FEM approximation ...
815 views

### Nonlinear dynamics: algorithm suggest

I've just started a thesis on nonlinear dynamics which entails numerical analysis of the Duffing oscillator (DO). It's basically just a second order ODE, or equivalently a set of ODEs. Say, after ...
3k views

### Schur's Complement and Inverse of Block Matrices

Assume that we are given a block matrix of the form: $$M = \left[ \begin{array}{cc} A & b \\ b^T & c \\ \end{array} \right]$$ where $b$ is a column vector. and $c$ is a scalar. Schur's ...
2k views

### Solving a simple Ax=b system in parallel with PETSc

I am new to the PETSc package. I have a ~4000x4000 matrix A in matrix-market format and I want to get PETSc to solve this using multiple processors. I know how to solve the system on a single ...
I know for a given matrix $M$, there exists a matrix $U$ over the integers with determinant $+1$ or $-1$ such that $UM=E$. I know $E$, but $M$ is not a square matrix. Is there any easy way to get \$...